A screw compressor of the related art is described for example in Japanese Unexamined Patent Application Publication No. 2005-163655 (Patent Literature 1). This technology of the related art includes: “a non-orbiting scroll member, an orbiting scroll member forming a suction chamber or a compression chamber by orbital motion engaging with the non-orbiting scroll member, a back pressure chamber to apply a pressing force against the non-orbiting scroll member to the scroll member, a back pressure chamber fluid inflow means to flow a fluid into the back pressure chamber to maintain the back pressure serving as the compression chamber pressure, and a back pressure chamber fluid outflow means to flow the inflow fluid into the suction chamber or back pressure chamber. The back pressure fluid outflow means includes in a series arrangement: a back pressure control valve to control the upstream and downstream pressure differential, and a throttle flow path, and an intermittent flow path intermittently connecting by way of the orbital motion of the orbiting scroll member along the back pressure chamber fluid outflow path connecting the back pressure chamber and suction chamber or compression chamber.